The present invention relates generally to perspective transformations, and more particularly, to a process for performing a perspective transformation from range-azimuth (B-scan) format to elevation-azimuth (C-scan) format.
A product known as a TMC 2301 image resampling sequencer manufactured by TRW LSI Products is available to perform image manipulation in video, graphics, medical, radar, and other image processing systems. It uses a 2nd order Taylor series to perform coordinate transformations from a Cartesian (x,y) format to a C-scan format. Together with another product known as a TMC 2330 coordinate transformer available from the same company, which transforms from B-scan format to Cartesian format, an approximation to the transformation from B-scan to C-scan formats can be achieved. These are VLSI products and typically used for real-time image warping, compression, and stretching and the like. They are capable of updating at greater than ten frames per second.
However, these products are not able to provide real-world image conformality for head-up displays, for example, because approximation errors grow to unacceptable levels when pitch and roll attitudes are introduced. Additionally, these products are not able to account for imaging delays. An approach to decouple the roll from the pitch attitude in the approximation requires a second TMC 2301 image resampling sequencer to separately perform the roll transformation. This approach, however, leads to cropping of the image comers and some nonconformality when pitch and roll attitudes are present. A newer TMC 2302 image resampling sequencer has been introduced that uses a 3rd order term in the Taylor series approximation. However, the increased accuracy from this approach does not meet the conformality requirements for processing data for head-up displays, and the like.
The transformation calculations in conventional processes have involved up to 53 arithmetic operations per pixel. To perform the transformation for a full set of display pixels in a near real time rate (&gt;10 frames/sec), it would require a dedicated VLSI image processor of which none are available. Currently available image processors are available to transform data in B-scan to a plan position indicator (PPI) format and have used. 2nd or 3rd order Taylor series approximation to do the transformation, but these suffer tremendous errors if they are used to transform data from B-scan to C-scan formats. These errors are fastest growing at shallower elevation angles and when vehicle roll are present. Other processors are available which try to simplify the transformation by decoupling the roll motion from the pitch and heading motions. An image from this type of processing when in a pitch and roll condition, typically is cropped at the corners and distorted from the real world image. The present invention overcomes the deficiencies of these conventional transformation processes.
Therefore, it is an objective of the present invention to provide an improved process for performing perspective transformations from range-azimuth (B-scan) format to elevation-azimuth (C-scan) format.